Long Xiaotian, the former king of the special forces, became a mercenary due to his brother's betrayal. In order to save his amnesia sister Liu Mingyue, he returned to the world to fight against the transnational criminal organization "Hellfire". In cooperation with the mysterious female killer Su Qing, the two went from testing each other to being dependent on each other for life and death, and jointly uncovered the shocking conspiracy behind the "zombie virus" and "alien technology", and eventually became the "kings of interstellar soldiers" guarding the earth.
